1. Field of the Invention
The invention relates to an apparatus and process for ultra-low pollutant emission combustion of fossil fuel using a primary combustion chamber with a relatively small amount of fuel and relatively low or high percentage of stoichiometric air requirement and a secondary combustion chamber with a large amount of fuel with excess air, both combustion chambers having cyclonic flow. The secondary combustion chamber is larger than the primary combustion chamber in a specified relation. A dilution chamber may be used. Combustion under these conditions results in ultra-low nitrogen oxides (NO.sub.x), carbon monoxide (CO) and total hydrocarbon emissions (THC).
2. Description of the Prior Art
Existing multi-stage combustors use nozzles to mix fuel and air within a combustion chamber and other existing designs use partially premixed fuel and air prior to introducing such fuel/air mixture into a combustion chamber. Other existing combustor designs which use fully premixed fuel and air prior to introducing the fuel/air mixture into a combustion chamber use a one-stage combustion process which does not provide high flame stability at very high excess air.
U.S. Pat. No. 4,112,676 teaches a combustor wherein a small portion of fuel is injected into the upstream end to form a fuel-rich air mixture for diffusion burning. A fuel-lean/air mixture is introduced through a plurality of axially spaced inlets of the burner to result in a series of low temperature premixed flames which provide reduced, thermally formed nitrogen oxide compounds. The '676 patent does not teach cyclonic flow through the combustion chambers.
U.S. Pat. No. 4,598,553 teaches a two-stage gas turbine combustor wherein fuel/air mixture is injected into the upstream combustion chamber from a first-stage swirl burner. The main downstream burner has a plurality of air inlets formed by a plurality of vanes which are disposed in an annular passage to swirl the air. When the flow rate of the supplied fuel is large, the fuel from the air inlets moves from an inner-peripheral surface toward the outer-peripheral surface of the second burner for better mixing.
U.S. Pat. No. 4,382,771 teaches a gas and steam generator having a plurality of progressively larger combustion chambers in communication through restrictive orifices. Fuel and air are introduced at the upstream end of two of three chambers and water is introduced downstream to produce saturated or superheated steam in combination with the products of combustion. The ratio of water to fuel is relatively high.
U.S. Pat. No. 4,385,490 teaches a staged combustor having a first combustion chamber and an adjacent and downstream larger diameter and volume second combustion chamber. All fuel is injected into the upstream end of the first combustion chamber. Air may be supplied tangentially to both combustion chambers reducing nitrogen oxide and carbon monoxide emissions.
U.S. Pat. No. 4,427,362 teaches a combustion method for reducing emissions of nitrogen oxides wherein all fuel is introduced into the first combustion zone with combustion occurring with combustion air in an amount of about 45 percent to 75 percent of the total stoichiometric amount of oxygen required for complete combustion of the fuel. Remaining fuel and combustion products are maintained at a temperature of at least 1800.degree. K. for a time sufficient to reduce the nitrogen oxides content of the mixture to a desired level following which air is added to one or more additional combustion zones for completion of combustion at a temperature of about 1600.degree. K. to 2000.degree. K.
U.S. Pat. No. 3,368,604 teaches a combustion device having two combustion chambers connected by a restriction orifice. All fuel is injected into the first combustion chamber and combustion air is introduced into both combustion chambers.
U.S. Pat. No. 4,651,534 teaches a gas turbine combustor having two stage combustion with all fuel injected at its upstream end. The second stage combustion zone has a larger cross section area than the first. 18 percent of the inlet air is introduced into each of the first and second combustion sections to mix with the fuel; 12 percent and 8 percent of the inlet air is introduced into the first combustion section and second combustion sections, respectively, to generate a swirling cooling flow; and the final 44 percent of the inlet air is introduced into the exhaust section to cool exhaust gases.
U.S Pat. No. 3,915,619 teaches a gas turbine combustor wherein separate streams of air are supplied to primary and secondary combustion zones for removing heat from the primary combustion zone and reintroducing the heat into the combustor at a region spaced downstream from both combustion zones. All of the fuel is introduced at the upstream end of the first combustion zone and into a swirling stream of air so as to effect controlled mixing of the fuel and air.
U.S. Pat. No. 4,021,186 teaches a two stage combustor wherein primary combustion occurs at sub-stoichiometric conditions in a primary combustion chamber. Air is injected at the outlet of the primary combustion chamber in such a manner that the air completely mixes with the flue gases leaving the primary combustion chamber thereby causing secondary combustion to occur within the furnace fire box or, alternatively, within the secondary combustion chamber.
U.S. Pat. No. 3,736,747 teaches a combustor having one combustion chamber with three separate combustion zones within a housing. All fuel is introduced into the upstream end of the first combustion zone and combusted in a fuel-rich flame. The flame is regeneratively cooled by air which swirls to contain and cool the flame.
U.S. Pat. No. 4,375,949 teaches a method of at least partially burning fuel introduced at an upstream end of the first stage of a two stage combustor. Fuel is partially burned in the first stage under conditions which reduce smoke and/or carbon and the partially combusted fuel is then brought into contact with a substantially non-volatile catalyst which is active for reducing the amount of nitrogen oxides in the partially combusted fuel.
U.S. Pat. No. 4,405,587 teaches a process for reducing the concentration of nitrogen oxides in a waste stream by burning with a stoichiometric deficiency of oxygen at a temperature between about 2000.degree. F. and about 3000.degree. F. to provide reducing conditions followed by oxidizing the combustibles present in the combustion effluent.